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Theranostics 2022; 12(11):5086-5102. doi:10.7150/thno.74989 This issue Cite

Research Paper

UBR5 promotes tumor immune evasion through enhancing IFN-γ-induced PDL1 transcription in triple negative breast cancer

Bingbing Wu¹, Mei Song^2*, Qun Dong^3*, Gang Xiang¹, Jing Li³, Xiaojing Ma^2✉, Fang Wei^1✉

1. Sheng Yushou Center of Cell Biology and Immunology, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Science and Biotechnology, Shanghai Jiao Tong University, Shanghai, China.
2. Department of Microbiology and Immunology, Weill Cornell Medicine, New York, New York.
3. Department of Bioinformatics and Biostatistics, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
^*Contribute equally to this work

✉ Corresponding author: Fang Wei, 800 Dongchuan Road, Minghang, Shanghai 200240, China. Phone: 86-21-34205287; Fax: 86-21-34205287; E-mail: fangweiedu.cn; Xiaojing Ma, xim2002cornell.edu

Abstract

Background: The up-regulation of PD-L1 is recognized as an adaption of cancer cells to evade immune surveillance and attack. However, the intrinsic mechanisms of the induction of PD-L1 by interferon-γ (IFN-γ) in tumor microenvironment remain incompletely characterized. Ubiquitin ligase E3 component N-recognition protein 5 (UBR5) has a critical role in tumorigenesis of triple negative breast cancer (TNBC) by triggering specific immune responses to the tumor. Dual targeting of UBR5 and PD-L1 exhibited superior therapeutic benefits in a preclinical TNBC model in short term.

Methods: The regulation of UBR5 to PD-L1 upon IFN-γ stimulation was evaluated through in UBR5 deficiency, reconstitution or overexpression cell line models by quantitative PCR, immunohistochemistry and RNA-seq. The effects of PD-L1 regulation by UBR5 and double blockade of both genes were evaluated in mouse TNBC model. Luciferase reporter assay, chromatin immunoprecipitation-qPCR and bioinformatics analysis were performed to explore the transcription factors involved in the regulation of UBR5 to PD-L1.

Results: E3 ubiquitin ligase UBR5 plays a key role in IFN-γ-induced PDL1 transcription in TNBC in an E3 ubiquitination activity-independent manner. RNA-seq-based transcriptomic analyses reveal that UBR5 globally affects the genes in the IFN-γ-induced signaling pathway. Through its poly adenylate binding (PABC) domain, UBR5 enhances the transactivation of PDL1 by upregulating protein kinase RNA-activated (PKR), and PKR's downstream factors including signal transducers and activators of transcription 1 (STAT1) and interferon regulatory factor 1 (IRF1). Restoration of PD-L1 expression in UBR5-deficient tumor cells recoups their malignancy in vivo, whereas CRISPR/Cas9-mediated simultaneous abrogation of UBR5 and PD-L1 expression yields synergistic therapeutic benefits than either blockade alone, with a strong impact on the tumor microenvironment.

Conclusions: This study identifies a novel regulator of PDL1 transcription, elucidates the underlying molecular mechanisms and provides a strong rationale for combination cancer immunotherapies targeting UBR5 and PD-L1.

Keywords: UBR5, Interferon-γ, PD-L1, PKR/STAT1/IRF1, triple negative breast cancer

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